...as the default Point ctor already zero-initializes its members, removing the
need for the memset call (that causes -Werror=class-memaccess, "clearing an
object of non-trivial type 'class Point'" with upcoming GCC 8).  Also use
unique_ptr.

Change-Id: Idc139b97e18c0d48079a14755124be72da91fb37
Reviewed-on: https://gerrit.libreoffice.org/48522Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>